To be honest WireGuard over Shadowsocks is neither common nor recommended, coz essentially it's TCP-over-TCP which will wreak havoc on TCP congestion control.
Unless you mean WireGuard over Shadowsocks UDP transport, but that is even less common.
Actually I'd rather WireGuard adopt some obfuscation mechanisms, but as Jason stated it's a non-goal and the focus is to get WireGuard into mainstream OS kernels. So the only hope is to provide some obfuscation transport underneath.
Tunneling WG over SS would be inefficient for obvious reasons. Maybe there should be a more lightweight solution.